Meaningful name for a routing process. This name must be unique
among all IP or Connectionless Network Service (CLNS) router
processes for a given router. If an area tag is not specified, a
null tag is assumed and the process is referenced with a null tag.
If an area tag is specified, output is limited to the specified
area. Required for multiarea IS-IS configuration. Optional for
conventional IS-IS configuration.

level-1

(Optional) Paths to all Level 1 routers in the area or areas in
which this router resides. The abbreviated keyword l1 may be used
in place of level-1.

level-2

(Optional) Paths to all Level 2 routers in the domain. The
abbreviated keyword l2 may be used in place of level-2.

host-nsap

(Optional) Host name or network service access point (NSAP) of
a router for which you would like to check reachability.

Command
Description:

To display a list of all connected routers in
all areas, use the show isis topology command in EXEC
mode.

Use the show isis topology EXEC command
to verify the presence and connectivity between all routers in all
areas.